This application claims the priority of Japanese Patent Application No. 3-229499 filed Aug. 15, 1991, which is incorporated herein by reference.
1. Field of the Invention
The present invention relates to ink jet recording paper and, more particularly, to fine paper type ink jet recording paper on which printed letters of high quality can be recorded.
2. Description of the Related Art
An ink jet recording method involves forcing ink to jet in the form of corpuscles using various mechanisms and making the ink corpuscles adhere to recording paper so as to record thereon patterns (including letters, characters and so on) in ink dots. Therefore, the method has advantages as that it can reduce generation of noise upon printing, can offer high quality full color recording and enables high-speed printing, compared with dot impact type recording methods in which typing dots are applied mechanically on recording paper.
On the other hand, ink used for ink jet recording has a defect that it is inferior in drying speed, because it is, in general, an aqueous ink containing direct dyes such as acid dyes.
Accordingly, ink jet recording paper must have the following characteristics:
(1) heighten the drying speed of ink dots adhering thereto, PA1 (2) ensure a high optical density of the printed patterns, and PA1 (3) causes little spread or running of the ink dots.
For the purpose of improving the foregoing characteristic (1), a measure to increase the ink absorbance of paper, or incorporation of silica having a great specific surface area into paper, has so then been taken. However, this measure has the defect that ink corpuscles applied to the recording paper into which silica is incorporated are absorbed thereinto with spreading, so that individual ink dots are enlarged in area and cause not only a drop in the optical density of a printed pattern but also blurring of the dots. Accordingly, it cannot meet the current needs of high image quality and high resolution.
In order to solve the above-described problem, recording papers have been prepared by coating various sizing agents, such as polyvinyl alcohol, polyvinyl pyrrolidone and the like, on the surface of the stock paper have been proposed, and have achieved good results.
On the other hand, neutral paper containing calcium carbonate as filler is prevailingly used as the stock for recording paper because of its superiorities in preservation and whiteness. However, such neutral paper also suffers from the disadvantages described below, because the pH thereof in cold water extraction is generally in the range of 9.0 to 10.0. That is, in a case where printing on said recording paper is carried out with aqueous ink comprising acid dyes or the like, the optical density of a printed pattern is low or the printed pattern lacks uniformity in quality, and also where full-color printing is carried out with a full-color ink jet printer each aqueous ink undergoes a change in color formability or the printed colors are discolored with a resultant failure in the faithful reproduction of the original colors.